The cleaning up of sites contaminated with hazardous or toxic waste has been recognized for some time as a major national environmental problem. There are, of course, many different conceptual approaches which have been attempted with varying degrees of success to clean such sites. One concept which has been successfully employed in the treatment of hazardous and/or toxic waste is to thermally clean such waste such as by pyrolysis and/or incineration. In fact, thermal methods are the only ways to dispose of certain wastes, such as chemical munitions, permanently.
Presently, the only successful thermal approach for cleaning a contaminated site has been to physically remove the soil from the site and truck the contaminated soil to a waste disposal site. At the waste disposal site, the soil is heated at elevated temperature and the contaminants within the soil are volatilized and then incinerated. Incineration processes and related equipment have been patterned closely after industrial equipment that has been developed for steam raising, cement making, heat treating and/or processing. Essentially, all such systems comprise either a rotary kiln where the soil is continuously fed by means of an archimedes screw through a cylinder which may be inclined or, alternatively, through a vertical shaft furnace or an inclined shaft furnace in which the soil is heated as a moving or fluidized bed as it falls by gravity through the furnace. All of these incineration processes combine continuous material handling, high temperature heating of materials, combustion of organic contaminants and cleaning of the resulting waste gas comprising distilled organics, etc. All such processes and equipment are designed based on the experiences and design guidelines used for heating of industrial materials which are, in most cases, consistent in size, shape and composition. Contaminated wastes, especially those generated over a long period of time by landfills or waste dumping from many different sources, are inconsistent in composition, size, shape and chemical make-up. Under these conditions, it becomes very difficult to design and operate a waste disposal system on a continuous, reliable and safe basis. In most instances, the disposal plant design requires substantial investment and equipment for sizing and controlled feeding of waste materials. However, decontamination of soils, of lagooned waste, of drums filled with hazardous waste and of bulky materials like contaminated tanks or other process equipment, present unique problems which render the cleansing of such matter not only difficult but in many instances impossible, at least on a commercial basis. This occurs not only because of inconsistencies in the feed, but also because certain "exotic" types of waste develop various chemical reactions which result in explosive mixtures that cannot be thermally disposed of by such continuous processes, at least not at the present time.
In such instances, the material must be segregated into small batches which are then heated within a box furnace in a closely controlled manner to distill or volatilize the organics (which are then subsequently incinerated) in a controlled process conventionally known in the trade as pyrolysis. Batch treatment of soils and non-pumpable sludges from contaminated waste sites is an expensive and impractical solution to the problem of cleansing such sites.
Contaminated soil and large lagoons, in theory, can best be treated by leaving the soil or the sludges in place, i.e. an in situ thermal cleaning system. There are no such systems at present. It is known that activity is being conducted by the Batelle Institute on an in situ thermal cleaning system which positions in the soil of the site a cathode and an anode. An electrical current is used to heat a plate in the soil interposed between the cathode and the anode which in turn is used to heat the soil and in the process thereof volatilize the organic material. However, there appear to be fundamental deficiencies in a cathode-anode arrangement, principally because the soil density is not uniform, for example the presence of rocks, boulders and the like as well as buried drums of waste etc., the non-uniform density of the site affects the ability of the cathode/anode to heat the plate. In addition, there may be inherent problems in generating sufficient heat from such an arrangement to sufficiently heat the site to its periphery.